Vehicles include an air conditioning system for cooling or heating a passenger compartment. The air conditioning system includes, as a configuration for a cooling system, a compressor, which compresses low-temperature and low-pressure gaseous refrigerant drawn from an evaporator into a high-temperature and high-pressure gaseous state, and sends it a condenser. Such compressors are classified into a mechanical type which rotates using an engine as a drive source to perform the compression, and an electric type which uses a motor as a drive source.
As shown in FIG. 1, an electric compressor includes a compression unit 100 which performs the compression, a motor unit 200 which drives the compression unit 100, and an inverter unit 300 which receives power from a battery of a vehicle and controls the rotation speed of the motor unit 200 to adjust the rate at which refrigerant is compressed.
As shown in FIGS. 2 and 3, the inverter unit 300 includes an inverter housing 330 which is coupled to a rear end of the motor unit 200, and an inverter which is provided in such a way that various circuit elements including a switching element (IGBT; Insulated Gate Bipolar Transistor) and a capacitor 320 are mounted on a printed circuit board (PCB) 310 in the inverter housing 330.
Because the switching element and the capacitor 320 of the inverter generate a large amount of heat, heat dissipation is required. Particularly, the capacitor 320 is largest among electronic parts of the inverter and is easily affected by surrounding environment compared to the other electronic parts. Hence, the capacitor 320 is one of the most critical factors in determining the lifetime of the inverter.
That is, despite the fact that the electric compressor is installed in an engine room and is under conditions of high ambient temperatures of 100° C. or more, heat dissipation has not been satisfactorily performed, thus greatly reducing the lifetime of the capacitor 320. For example, the conventional capacitor 320 may be fixed to the inverter housing 330 by a fixing adhesive such as silicon. In this case, the heat dissipation performance greatly deteriorates due to the adhesive, whereby the lifetime of the capacitor 320 is shortened.
Furthermore, a flow rate of ripple current that flows through the capacitor 320 frequently increases over an allowable value of the capacitor 320, thus further shortening the lifetime of the capacitor 320. This leads to shortening of the lifetime of the inverter.
Previously, as the electric compressor has been used for extremely limited purposes, there has been no problem even though special measures for increasing the lifetime of the inverter of the electric compressor are not taken. However, as the range of use of the electric compressor is gradually expanded for purposes of a heat pump mode, an increase in rated voltage, etc., the factor of securing the reliability in lifetime becomes increasingly important.